Soil characterisation to investigate the role of the burial environment in archaeological glass alteration.

Abstract

This thesis project is focused on the direct interactions between ancient glass objects and the soils where they were buried. The thesis aims to clarify the mechanism of ancient glass alteration. The physical-chemical properties, as well as the alteration patinas, of Roman glasses, found in the archaeological site of Aquileia (north of Italy), were investigated through Optical and Scanning Electron Microscopy (SEM-EDS) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). On parallel, the chemistry and the physical properties of the environmental soils, corresponding to the site of the archaeological findings, were studied in terms of elemental composition, though Microwave Plasma Atomic Emission Spectroscopy (MP-AES), and characterized through ion-exchange capacity, conductivity and pH measurements.

Archaeological glass fragments developed alteration patterns – mainly pitting and iridescence, as well as discolouration - consistent with the centuries-long placement in burial environment. Specifically, the soil parameters considered with the intrinsic features of glasses explain the formation of different degradation marks on glass surface. The pH level of the soil and the cation exchange capacity resulted crucial in glass degradation. In particular, the glass samples with the highest degree of deterioration are associated to environmental soils characterized by low pH values and high cation exchange capacities.